This invention relates to a method for sawing hard material with circular abrasive disc saws of the kind having secured to the periphery of the disc arcuated cutting segments of bonded diamond abrasives.
The present-day art of sawing granite or hard rock in general, does not allow large-depth cuts to be made in a single pass for various reasons which will be described hereinafter, and this operation is carried out by a succession of small-depth passes.
The great advantages obtained by cutting marble and soft rock with diamond discs and diamond bladed frames in a single deep pass are, on the other hand, well known.
To overcome this difficulty with hard stone, the art has directed itself towards a search for new sawing methods using diamond discs or blades, but the results up to the present time have been poor because of various problems which have arisen.
Such rock is sawn with machines provided with disc tools comprising on their peripheral rim a plurality of teeth on which arcuated cutting segments are carried, consisting of bonded abrasive material, normally a sintered material, containing preferably diamonds of various concentrations and sizes, supported by a binder of suitable hardness.
In practice, in the present-day art, the concentration of the diamond present in the cutting element is increased and the resistance of the binder is reduced in accordance with the hardness of the material to be cut, i.e. the greater the hardness, the greater the diamond concentration.
In this manner, the diamonds on the cutting surface are quickly renewed, and thus the cutting surface itself is rapidly self-sharpening. This evidently leads to rapid wear of the tools and consequent high manufacturing costs. However as soon as harder binders were used it was found that the cutting surface tended to flatten off and become clogged, and in order to re-sharpen it the pressure exerted by the machine on the block to be cut had to be increased. This increase in pressure resulted in a stress increase in the metal core of the disc, which became subjected to a point load.
The stress limits are obviously related to the thickness of the metal core, and if the diameter of the disc or the load are increased in order to make deep passes, the thickness of the metal core must also be increased. The primary disadvantage of this increase in thickness is the need to provide wider and therefore more costly cutting segments, and a further considerable disadvantage is the greater loss of material in the cutting operation and a corresponding reduction in the use ratio of the material itself, which results in a cost increase of the final product.
Furthermore, the core thickness is not conditional on the mechanical strength as such, because the stage which precedes the actual fracture, consisting in the elastic deformation of the disc, is itself not acceptable. In this case, the surfaces obtained would be no longer flat but undulated, and subsequent facing operations would be necessary.
The known art is evidently more extensive than this, and an attempt has been made to exemplify it briefly to show the problems concerned.
More information as to the problems incountered in using abrasive discs for cutting hard rocks are found in publications of large manufacturing companies such as De Beers or the publication Granit International sponsored by Ernst Winter and Sohn GmbH & Co. of Hamburg West Germany, or from catalogues of these companies in which instructions are given to the users of the diamond discs.
The main object of the present invention is to eliminate the aforementioned disadvantages of the known art by providing a method of cutting hard material such as granite or hard rock with abrasive disc saws which allows a deep cut in a single pass to be made, and which gives a finished product not requiring further facing operations.
A further object is to provide a method through which the cutting edge become self-sharpening without requiring excessive working loads, so giving long life to the cutting edges.
A further object is to provide a method in which discs with a small thickness core may be used, even in case of discs of large diameter, leading to cutting segments of small cross-section and low material losses during working.
A further object is to provide a method in which good diamond utilisation and an economical cutting operation is obtained, and which may be used with the usual machines normally available on sites of this type.
Applicant has found that contrary to the general belief according to which in the case of hard rocks such as granites the concentration of diamonds should increase with the increase in the cutting depth of the disc, such concentration should instead be decreased with the increase in the cutting depth, when all other conditions of the cutting operation are maintained unchanged when the starting concentration is adequate for small depths cuts.
The problem to be solved was therefore to find out the optimum diamond concentration for a given cutting depth.